Torkild Tveraa - Academia.edu (original) (raw)
Papers by Torkild Tveraa
Tveraa, T., Stien, A. & Langeland, K. 2016. Updated figures of carnivore damages on semi domestic... more Tveraa, T., Stien, A. & Langeland, K. 2016. Updated figures of carnivore damages on semi domestic reindeer – NINA Report 1248. 28 pp. As a part of a possible change in the compensation system for semi-domestic reindeer lost to carnivores, NINA has been asked to estimate the costs related to losses. A premise has been that the compensation shall secure full compensation for direct costs as well as the indirect cost that are associated with losses of females. Full compensation refers to the value that the reindeer herder would obtain if the animal was slaughtered, plus subsidies. For losses of females killed by carnivores, the compensation should also include the costs that are associated with the replacement of that female. I.e. a female calf that could otherwise have been slaughtered need to be kept to replace the female. In the current calculation, the indirect costs are set equal to the value of two slaughtered calves. A premise for our task has been to identify the real value of ...
Oecologia, 2003
A central issue in ecology is to what extent food limitation and predation affect animal populati... more A central issue in ecology is to what extent food limitation and predation affect animal populations. We studied how survival and reproductive success was related to the female , s size in a population of semi-domesticated reindeer during 2 years where there was a large difference in snowfall during winter. The females were kept within a predator-free enclosure for about 5 weeks during the calving period and thereafter released to their natural summer pastures. Small females were more likely to fail to reproduce and they produced smaller calves than large females. Additionally, small females were more likely to loose their calves due to starvation within the predator-free enclosure and to predators outside the enclosure. Food limitation during the harsh winter appeared to be the major cause of deaths. However, food limitation interacted with predation and led to high calf losses when the females experienced low food availability during the harsh winter. In contrast, predators killed no calves after the mild winter. Apparently, the interaction between predation and food limitation is due to small females favouring their own growth and survival over calf production in summers following harsh winters with food shortage. Our results indicate that a compensatory relationship exists between mortality due food limitation and predation. Thus, the impact of calf predation on reindeer demography and population dynamics may be limited.
Journal of Animal Ecology, 2015
1. Exploitation of living marine resources has resulted in major changes to populations of target... more 1. Exploitation of living marine resources has resulted in major changes to populations of targeted species and functional groups of large-bodied species in the ocean.
1 NINAs publikasjoner NINA Rapport Dette er en ny, elektronisk serie fra 2005 som erstatter de ti... more 1 NINAs publikasjoner NINA Rapport Dette er en ny, elektronisk serie fra 2005 som erstatter de tidligere seriene NINA Fagrapport, NINA Oppdragsmelding og NINA Project Report. Normalt er dette NINAs rapportering til oppdragsgiver etter gjennomført forsknings-, overvåkings-eller utredningsarbeid. I tillegg vil serien favne mye av instituttets øvrige rapportering, for eksempel fra seminarer og konferanser, resultater av eget forsknings-og utredningsarbeid og litteraturstudier. NINA Rapport kan også utgis på annet språk når det er hensiktsmessig.
Ecology and Evolution, 2014
For long-lived organisms, the fitness value of survival is greater than that of current reproduct... more For long-lived organisms, the fitness value of survival is greater than that of current reproduction. Asymmetric fitness rewards suggest that organisms inhabiting unpredictable environments should adopt a risk-sensitive life history, predicting that it is adaptive to allocate resources to increase their own body reserves at the expense of reproduction. We tested this using data from reindeer populations inhabiting contrasting environments and using winter body mass development as a proxy for the combined effect of winter severity and density dependence. Individuals in good and harsh environments responded similarly: Females who lost large amounts of winter body mass gained more body mass the coming summer compared with females losing less mass during winter. Additionally, females experienced a cost of reproduction: On average, barren females gained more body mass than lactating females. Winter body mass development positively affected both the females' reproductive success and offspring body mass. Finally, we discuss the relevance of our findings with respect to scenarios for future climate change.
Human Ecology, 2011
Previously it has been found that an important risk buffering strategy in the Saami reindeer husb... more Previously it has been found that an important risk buffering strategy in the Saami reindeer husbandry in Norway is the accumulation of large herds of reindeer as this increases long-term household viability. Nevertheless, few studies have investigated how official policies, such as economic compensation for livestock losses, can influence pastoral strategies. This study investigated the effect of received predation compensation on individual husbandry units' future herd size. The main finding in this study is that predation compensation had a positive effect on husbandry units' future herd size. The effect of predation compensation, however, was nonlinear in some years, indicating that predation compensation had a positive effect on future herd size only up to a certain threshold whereby adding additional predation compensation had little effect on future herd size. More importantly, the effect of predation compensation was positive after controlling for reindeer density, indicating that for a given reindeer density husbandry units receiving more predation compensation performed better (measured as the size of future herds) compared to husbandry units receiving less compensation.
In wild animal population studies, capture heterogeneity is likely to be prevalent and can reduce... more In wild animal population studies, capture heterogeneity is likely to be prevalent and can reduce the accuracy of vital rate estimates. Here, we test how individual detection probabilities vary through the breeding season in a population of a cliff-nesting colonial seabird, the Black-legged Kittiwake (Rissa tridactyla). Specifically, we expected detection probability to be affected by changes in brooding behavior and nest attendance associated with the breeding phenology and the local breeding performance of individuals. As predicted, we found that strong heterogeneities in detection probability can occur in relation to the breeding performance of individuals, the breeding performance of their neighbors, and the timing of surveys. Detection probability is highest and most homogeneous at the beginning of the breeding season. Later in the season, it is lower and can vary dramatically among groups of breeding individuals. A simulation approach was used to assess the implications of these results for the performance (bias and precision) of different study designs. Clearly, investing sampling effort early in the season is an efficient way to improve the accuracy of parameter estimates in this species. Our findings stress the importance of establishing study designs that take into account the population and behavioral ecology of the focal species.
The Journal of applied ecology, 2014
A major challenge in biodiversity conservation is to facilitate viable populations of large apex ... more A major challenge in biodiversity conservation is to facilitate viable populations of large apex predators in ecosystems where they were recently driven to ecological extinction due to resource conflict with humans.Monetary compensation for losses of livestock due to predation is currently a key instrument to encourage human-carnivore coexistence. However, a lack of quantitative estimates of livestock losses due to predation leads to disagreement over the practice of compensation payments. This disagreement sustains the human-carnivore conflict.The level of depredation on year-round, free-ranging, semi-domestic reindeer by large carnivores in Fennoscandia has been widely debated over several decades. In Norway, the reindeer herders claim that lynx and wolverine cause losses of tens of thousands of animals annually and cause negative population growth in herds. Conversely, previous research has suggested that monetary predator compensation can result in positive population growth in ...
Human Ecology, 2009
While there is a general assumption that labor has a positive effect on pastoral production, stud... more While there is a general assumption that labor has a positive effect on pastoral production, studies that have tried to quantify this relationship have found no effects. This is most likely because these studies have been looking for effects only at the household level of social organization, although it is well documented that nomadic pastoralist households share and exchange labor in socalled cooperative herding groups. This study investigates possible labor related effects on production among Saami reindeer herders in northern Norway and whether these effects are scale dependent. Contrary to previous studies, we found both a general effect of labor on Saami reindeer husbandry production and the presence of a scale dependent effect, i.e., the more robust results were found on the level of social organization where cooperative herding is undertaken.
Journal of Experimental Biology, 2003
Understanding the role and operation of top predators, such as seabirds, in marine systems requir... more Understanding the role and operation of top predators, such as seabirds, in marine systems requires investigation of their diet and feeding ecology. Knowledge of foraging patterns is essential when responding to many practical and theoretical questions related to marine ecology, behavioural ecology, ecophysiology and the management and conservation of marine ecosystems (Ashmole
Proceedings of the Royal Society B: Biological Sciences, 2001
Mothers are predicted to invest in their offspring depending on the quality of their mate, their ... more Mothers are predicted to invest in their offspring depending on the quality of their mate, their opportunity to invest in future reproduction and the characteristics of the habitat in which their offspring will be born. Recent studies have suggested a transfer of maternal immunity to offspring as an induced response to the local presence of parasites in the environment, but evidence has been indirect. Here, we show the presence of antibodies against the Lyme disease agent Borrelia burgdorferi sensu lato, a spirochaete transmitted by the seabird tick Ixodes uriae, in the eggs of kittiwakes Rissa tridactyla. We report higher prevalence of antibodies against Borrelia in eggs from breeding areas with higher prevalence and abundance of ticks. Further, high repeatabilities of antibody-positive eggs within clutches and between first and replacement clutches show that, within a breeding season, females differ consistently with respect to the expression of this induced maternal response. Our results suggest that mothers can alter investment in their young depending on local conditions. Such maternal effects clearly have implications for the ecology and evolution of host-parasite interactions.
Polar Biology, 2005
In birds, the characteristics of the nest site may affect reproductive success. We found that she... more In birds, the characteristics of the nest site may affect reproductive success. We found that shelter is an important characteristic of the Antarctic petrel (Thalassoica antarctica) nests because shelter prevents chick predation. However, the benefit of shelter was countervailed by melt water which mainly entered well-sheltered nests. Chick survival was monitored until the chick was left unattended for the first
Polar Biology, 2001
We studied several aspects of the foraging ecology of fulmars rearing young chicks on Bjùrnùya.
Oikos, 2007
It has been suggested that animals may escape attack from mobile parasites by aggregating in self... more It has been suggested that animals may escape attack from mobile parasites by aggregating in selfish herds. A selfish herd disperses the risk of being attacked among its members and the per individual risk of parasite infection should therefore decrease with increasing animal density through the encounter Ádilution effect. Moreover, in a selfish herd, dominant and agile animals should occupy the best positions and thereby receive fewer attacks compared to lower ranked animals at the periphery. We tested these predictions on reindeer (Rangifer tarandus tarandus ) parasitized by warble flies (Hypoderma tarandi ). Warble flies oviposit their eggs on reindeer during summer and induce strong anti-parasitic behavioural responses in the herds. In this period, reindeer are sexually segregated; females and calves form large and dense herds while males are more solitary. After hatching, the warble fly larvae migrate under the skin of their host where they encyst. In the present study encysted larvae were counted on newly slaughtered hides of male calves and 1.5 year old males from 18 different reindeer herds in Finnmark, northern Norway with large contrasts in reindeer density. In reindeer, body mass is correlated with fitness and social status and we hypothesized that individual carcass mass reflected the animal's ability to occupy the best positions within the herd. Larval abundance was higher among the 1.5 year old males than among the calves. For calves we found in accordance with the selfish herd hypothesis a negative relationship between larval abundance and animal density and between larval abundance and body mass. These relationships were absent for the 1.5 year old males. We suggest that these differences were due to different grouping behaviour where calves and females, but not males, aggregated in selfish herds where they escaped parasitism.
Oikos, 2007
... Torkild Tveraa,; Per Fauchald,; Nigel Gilles Yoccoz,; Rolf Anker Ims,; Ronny Aanes,; Kjell Ar... more ... Torkild Tveraa,; Per Fauchald,; Nigel Gilles Yoccoz,; Rolf Anker Ims,; Ronny Aanes,; Kjell Arild Høgda. ... A recent study revealed that the remaining predators (wolverine-Gulo gulo, red fox-Vulpes vulpes, lynx-Lynx lynx and golden eagle-Aquila chrysaetos) affect mortality of reindeer ...
Oikos, 2004
Life histories are state-dependent, and an individual&amp... more Life histories are state-dependent, and an individual's reproductive decisions are determined by its available resources and the needs of its offspring. Here we test how a chick's needs for food and protection influence parental decisions in the Antarctic petrel, Thalassoica antarctica , where the parents, due to their long breeding lifespan, are expected to give priority to their own needs
Oikos, 2009
In a previous experiment we have documented that organisms adopt a risk-sensitive reproductive al... more In a previous experiment we have documented that organisms adopt a risk-sensitive reproductive allocation when summer reproductive investment competes with survival in the coming winter ). This tradeoff is present through autumn female body mass, which acts as an insurance against unpredictable winter environmental conditions. We tested this hypothesis experimentally on female reindeer experiencing stable and benign winter feeding conditions. Additional supplementary feeding and removal of newborns represented two sets of experimental manipulations. Females in the supplementary feeding group increased more in winter body mass relative to control females. This manipulation, however, did not have any effect on summer body mass development for neither females nor offspring, but we found a positive effect of feeding on offspring birth mass for smaller females. In contrast, offspring removal did have a positive effect on summer body mass development as females in this group were larger in the autumn relative to control females. In essence, we documented two immediate effects as: (1) supplementary feeding did have a positive effect on spring body mass for smaller females; and (2) offspring removal did increase the female summer somatic growth as this had a positive effect on female autumn body mass. Additionally, we tested for lagged effects, but we could not document any biologically significant effects of neither manipulation in the coming spring. The fact that we only found rather weak effects of both manipulations was as expected for risk sensitive individuals experiencing benign environmental conditions over many years.
Oecologia, 1995
We examined the effect of natural clutch size on the cost of incubation in a population of common... more We examined the effect of natural clutch size on the cost of incubation in a population of common eiders Somateria mollissima nesting in Tromsø, northern Norway. The body condition of females at day 5 in the incubation period was not related to clutch size (3–6 eggs), but females incubating large clutches lost more mass and had a lower body condition
Tveraa, T., Stien, A. & Langeland, K. 2016. Updated figures of carnivore damages on semi domestic... more Tveraa, T., Stien, A. & Langeland, K. 2016. Updated figures of carnivore damages on semi domestic reindeer – NINA Report 1248. 28 pp. As a part of a possible change in the compensation system for semi-domestic reindeer lost to carnivores, NINA has been asked to estimate the costs related to losses. A premise has been that the compensation shall secure full compensation for direct costs as well as the indirect cost that are associated with losses of females. Full compensation refers to the value that the reindeer herder would obtain if the animal was slaughtered, plus subsidies. For losses of females killed by carnivores, the compensation should also include the costs that are associated with the replacement of that female. I.e. a female calf that could otherwise have been slaughtered need to be kept to replace the female. In the current calculation, the indirect costs are set equal to the value of two slaughtered calves. A premise for our task has been to identify the real value of ...
Oecologia, 2003
A central issue in ecology is to what extent food limitation and predation affect animal populati... more A central issue in ecology is to what extent food limitation and predation affect animal populations. We studied how survival and reproductive success was related to the female , s size in a population of semi-domesticated reindeer during 2 years where there was a large difference in snowfall during winter. The females were kept within a predator-free enclosure for about 5 weeks during the calving period and thereafter released to their natural summer pastures. Small females were more likely to fail to reproduce and they produced smaller calves than large females. Additionally, small females were more likely to loose their calves due to starvation within the predator-free enclosure and to predators outside the enclosure. Food limitation during the harsh winter appeared to be the major cause of deaths. However, food limitation interacted with predation and led to high calf losses when the females experienced low food availability during the harsh winter. In contrast, predators killed no calves after the mild winter. Apparently, the interaction between predation and food limitation is due to small females favouring their own growth and survival over calf production in summers following harsh winters with food shortage. Our results indicate that a compensatory relationship exists between mortality due food limitation and predation. Thus, the impact of calf predation on reindeer demography and population dynamics may be limited.
Journal of Animal Ecology, 2015
1. Exploitation of living marine resources has resulted in major changes to populations of target... more 1. Exploitation of living marine resources has resulted in major changes to populations of targeted species and functional groups of large-bodied species in the ocean.
1 NINAs publikasjoner NINA Rapport Dette er en ny, elektronisk serie fra 2005 som erstatter de ti... more 1 NINAs publikasjoner NINA Rapport Dette er en ny, elektronisk serie fra 2005 som erstatter de tidligere seriene NINA Fagrapport, NINA Oppdragsmelding og NINA Project Report. Normalt er dette NINAs rapportering til oppdragsgiver etter gjennomført forsknings-, overvåkings-eller utredningsarbeid. I tillegg vil serien favne mye av instituttets øvrige rapportering, for eksempel fra seminarer og konferanser, resultater av eget forsknings-og utredningsarbeid og litteraturstudier. NINA Rapport kan også utgis på annet språk når det er hensiktsmessig.
Ecology and Evolution, 2014
For long-lived organisms, the fitness value of survival is greater than that of current reproduct... more For long-lived organisms, the fitness value of survival is greater than that of current reproduction. Asymmetric fitness rewards suggest that organisms inhabiting unpredictable environments should adopt a risk-sensitive life history, predicting that it is adaptive to allocate resources to increase their own body reserves at the expense of reproduction. We tested this using data from reindeer populations inhabiting contrasting environments and using winter body mass development as a proxy for the combined effect of winter severity and density dependence. Individuals in good and harsh environments responded similarly: Females who lost large amounts of winter body mass gained more body mass the coming summer compared with females losing less mass during winter. Additionally, females experienced a cost of reproduction: On average, barren females gained more body mass than lactating females. Winter body mass development positively affected both the females' reproductive success and offspring body mass. Finally, we discuss the relevance of our findings with respect to scenarios for future climate change.
Human Ecology, 2011
Previously it has been found that an important risk buffering strategy in the Saami reindeer husb... more Previously it has been found that an important risk buffering strategy in the Saami reindeer husbandry in Norway is the accumulation of large herds of reindeer as this increases long-term household viability. Nevertheless, few studies have investigated how official policies, such as economic compensation for livestock losses, can influence pastoral strategies. This study investigated the effect of received predation compensation on individual husbandry units' future herd size. The main finding in this study is that predation compensation had a positive effect on husbandry units' future herd size. The effect of predation compensation, however, was nonlinear in some years, indicating that predation compensation had a positive effect on future herd size only up to a certain threshold whereby adding additional predation compensation had little effect on future herd size. More importantly, the effect of predation compensation was positive after controlling for reindeer density, indicating that for a given reindeer density husbandry units receiving more predation compensation performed better (measured as the size of future herds) compared to husbandry units receiving less compensation.
In wild animal population studies, capture heterogeneity is likely to be prevalent and can reduce... more In wild animal population studies, capture heterogeneity is likely to be prevalent and can reduce the accuracy of vital rate estimates. Here, we test how individual detection probabilities vary through the breeding season in a population of a cliff-nesting colonial seabird, the Black-legged Kittiwake (Rissa tridactyla). Specifically, we expected detection probability to be affected by changes in brooding behavior and nest attendance associated with the breeding phenology and the local breeding performance of individuals. As predicted, we found that strong heterogeneities in detection probability can occur in relation to the breeding performance of individuals, the breeding performance of their neighbors, and the timing of surveys. Detection probability is highest and most homogeneous at the beginning of the breeding season. Later in the season, it is lower and can vary dramatically among groups of breeding individuals. A simulation approach was used to assess the implications of these results for the performance (bias and precision) of different study designs. Clearly, investing sampling effort early in the season is an efficient way to improve the accuracy of parameter estimates in this species. Our findings stress the importance of establishing study designs that take into account the population and behavioral ecology of the focal species.
The Journal of applied ecology, 2014
A major challenge in biodiversity conservation is to facilitate viable populations of large apex ... more A major challenge in biodiversity conservation is to facilitate viable populations of large apex predators in ecosystems where they were recently driven to ecological extinction due to resource conflict with humans.Monetary compensation for losses of livestock due to predation is currently a key instrument to encourage human-carnivore coexistence. However, a lack of quantitative estimates of livestock losses due to predation leads to disagreement over the practice of compensation payments. This disagreement sustains the human-carnivore conflict.The level of depredation on year-round, free-ranging, semi-domestic reindeer by large carnivores in Fennoscandia has been widely debated over several decades. In Norway, the reindeer herders claim that lynx and wolverine cause losses of tens of thousands of animals annually and cause negative population growth in herds. Conversely, previous research has suggested that monetary predator compensation can result in positive population growth in ...
Human Ecology, 2009
While there is a general assumption that labor has a positive effect on pastoral production, stud... more While there is a general assumption that labor has a positive effect on pastoral production, studies that have tried to quantify this relationship have found no effects. This is most likely because these studies have been looking for effects only at the household level of social organization, although it is well documented that nomadic pastoralist households share and exchange labor in socalled cooperative herding groups. This study investigates possible labor related effects on production among Saami reindeer herders in northern Norway and whether these effects are scale dependent. Contrary to previous studies, we found both a general effect of labor on Saami reindeer husbandry production and the presence of a scale dependent effect, i.e., the more robust results were found on the level of social organization where cooperative herding is undertaken.
Journal of Experimental Biology, 2003
Understanding the role and operation of top predators, such as seabirds, in marine systems requir... more Understanding the role and operation of top predators, such as seabirds, in marine systems requires investigation of their diet and feeding ecology. Knowledge of foraging patterns is essential when responding to many practical and theoretical questions related to marine ecology, behavioural ecology, ecophysiology and the management and conservation of marine ecosystems (Ashmole
Proceedings of the Royal Society B: Biological Sciences, 2001
Mothers are predicted to invest in their offspring depending on the quality of their mate, their ... more Mothers are predicted to invest in their offspring depending on the quality of their mate, their opportunity to invest in future reproduction and the characteristics of the habitat in which their offspring will be born. Recent studies have suggested a transfer of maternal immunity to offspring as an induced response to the local presence of parasites in the environment, but evidence has been indirect. Here, we show the presence of antibodies against the Lyme disease agent Borrelia burgdorferi sensu lato, a spirochaete transmitted by the seabird tick Ixodes uriae, in the eggs of kittiwakes Rissa tridactyla. We report higher prevalence of antibodies against Borrelia in eggs from breeding areas with higher prevalence and abundance of ticks. Further, high repeatabilities of antibody-positive eggs within clutches and between first and replacement clutches show that, within a breeding season, females differ consistently with respect to the expression of this induced maternal response. Our results suggest that mothers can alter investment in their young depending on local conditions. Such maternal effects clearly have implications for the ecology and evolution of host-parasite interactions.
Polar Biology, 2005
In birds, the characteristics of the nest site may affect reproductive success. We found that she... more In birds, the characteristics of the nest site may affect reproductive success. We found that shelter is an important characteristic of the Antarctic petrel (Thalassoica antarctica) nests because shelter prevents chick predation. However, the benefit of shelter was countervailed by melt water which mainly entered well-sheltered nests. Chick survival was monitored until the chick was left unattended for the first
Polar Biology, 2001
We studied several aspects of the foraging ecology of fulmars rearing young chicks on Bjùrnùya.
Oikos, 2007
It has been suggested that animals may escape attack from mobile parasites by aggregating in self... more It has been suggested that animals may escape attack from mobile parasites by aggregating in selfish herds. A selfish herd disperses the risk of being attacked among its members and the per individual risk of parasite infection should therefore decrease with increasing animal density through the encounter Ádilution effect. Moreover, in a selfish herd, dominant and agile animals should occupy the best positions and thereby receive fewer attacks compared to lower ranked animals at the periphery. We tested these predictions on reindeer (Rangifer tarandus tarandus ) parasitized by warble flies (Hypoderma tarandi ). Warble flies oviposit their eggs on reindeer during summer and induce strong anti-parasitic behavioural responses in the herds. In this period, reindeer are sexually segregated; females and calves form large and dense herds while males are more solitary. After hatching, the warble fly larvae migrate under the skin of their host where they encyst. In the present study encysted larvae were counted on newly slaughtered hides of male calves and 1.5 year old males from 18 different reindeer herds in Finnmark, northern Norway with large contrasts in reindeer density. In reindeer, body mass is correlated with fitness and social status and we hypothesized that individual carcass mass reflected the animal's ability to occupy the best positions within the herd. Larval abundance was higher among the 1.5 year old males than among the calves. For calves we found in accordance with the selfish herd hypothesis a negative relationship between larval abundance and animal density and between larval abundance and body mass. These relationships were absent for the 1.5 year old males. We suggest that these differences were due to different grouping behaviour where calves and females, but not males, aggregated in selfish herds where they escaped parasitism.
Oikos, 2007
... Torkild Tveraa,; Per Fauchald,; Nigel Gilles Yoccoz,; Rolf Anker Ims,; Ronny Aanes,; Kjell Ar... more ... Torkild Tveraa,; Per Fauchald,; Nigel Gilles Yoccoz,; Rolf Anker Ims,; Ronny Aanes,; Kjell Arild Høgda. ... A recent study revealed that the remaining predators (wolverine-Gulo gulo, red fox-Vulpes vulpes, lynx-Lynx lynx and golden eagle-Aquila chrysaetos) affect mortality of reindeer ...
Oikos, 2004
Life histories are state-dependent, and an individual&amp... more Life histories are state-dependent, and an individual's reproductive decisions are determined by its available resources and the needs of its offspring. Here we test how a chick's needs for food and protection influence parental decisions in the Antarctic petrel, Thalassoica antarctica , where the parents, due to their long breeding lifespan, are expected to give priority to their own needs
Oikos, 2009
In a previous experiment we have documented that organisms adopt a risk-sensitive reproductive al... more In a previous experiment we have documented that organisms adopt a risk-sensitive reproductive allocation when summer reproductive investment competes with survival in the coming winter ). This tradeoff is present through autumn female body mass, which acts as an insurance against unpredictable winter environmental conditions. We tested this hypothesis experimentally on female reindeer experiencing stable and benign winter feeding conditions. Additional supplementary feeding and removal of newborns represented two sets of experimental manipulations. Females in the supplementary feeding group increased more in winter body mass relative to control females. This manipulation, however, did not have any effect on summer body mass development for neither females nor offspring, but we found a positive effect of feeding on offspring birth mass for smaller females. In contrast, offspring removal did have a positive effect on summer body mass development as females in this group were larger in the autumn relative to control females. In essence, we documented two immediate effects as: (1) supplementary feeding did have a positive effect on spring body mass for smaller females; and (2) offspring removal did increase the female summer somatic growth as this had a positive effect on female autumn body mass. Additionally, we tested for lagged effects, but we could not document any biologically significant effects of neither manipulation in the coming spring. The fact that we only found rather weak effects of both manipulations was as expected for risk sensitive individuals experiencing benign environmental conditions over many years.
Oecologia, 1995
We examined the effect of natural clutch size on the cost of incubation in a population of common... more We examined the effect of natural clutch size on the cost of incubation in a population of common eiders Somateria mollissima nesting in Tromsø, northern Norway. The body condition of females at day 5 in the incubation period was not related to clutch size (3–6 eggs), but females incubating large clutches lost more mass and had a lower body condition